get all the duplicate elements from array javascript code example
Example 1: javascript find duplicate in array
// JavaScript - finds if there is duplicate in an array.
// Returns True or False.
const isThereADuplicate = function(arrayOfNumbers) {
// Create an empty associative array or hash.
// This is preferred,
let counts = {};
// // but this also works. Comment in below and comment out above if you want to try.
// let counts = [];
for(var i = 0; i <= arrayOfNumbers.length; i++) {
// As the arrayOfNumbers is being iterated through,
// the counts hash is being populated.
// Each value in the array becomes a key in the hash.
// The value assignment of 1, is there to complete the hash structure.
// Once the key exists, meaning there is a duplicate, return true.
// If there are no duplicates, the if block completes and returns false.
if(counts[arrayOfNumbers[i]] === undefined) {
counts[arrayOfNumbers[i]] = 1;
} else {
return true;
}
}
return false;
}
Example 2: how to get duplicate values from array in javascript
const arr = ["q", "w", "w", "e", "i", "u", "r"]
arr.reduce((acc, cur) => {
if(acc[cur]) {
acc.duplicates.push(cur)
} else {
acc[cur] = true //anything could go here
}
}, { duplicates: [] })